1. Field of the Invention
The present invention relates to a hole plugging method for printed circuit boards, a hole plugging device which carries out such method and a manufacturing method in accordance, and particularly, to a hole plugging method for printed circuit board and to a hole plugging device and a manufacturing method in accordance therewith which plugs holes in a printed circuit board with an insulating resin or solder resist by abutting a squeegee or doctor blade to an exposed hole using a mask capable of exposing a certain portion of a board or plugs resin or solder resist between circuit patterns with.
2. Description of the Background Art
Recently, integrated circuits (IC) have become more densified by an increase in the degree of integration according to the development of technology. Accordingly, it is required that a printed circuit board for mounting ICs become more densified.
For meeting this necessity, currently, the printed circuit board is densified by fabricating a multi layer (printed circuit) board formed with a plurality of layers. In the multi layer board 1, open through holes 1d and via blind holes 1c may be form in the board wherein a conductive layer 1e is coated in the holes 1c and 1d to electrically interconnect circuit patterns 1a and 1b of one or more an inner layers and/or the surface layers, with reference to FIG. 1A.
The through hole 1d has a relatively large diameter than the via hole 1c and is typically formed by employing a mechanical process such as by drilling. However, the interval between the through holes 1d can not be narrowed beyond a certain spacing and there is thus a limitation in the densification degree of the board when the sizes of tools and avoidance of damage to the board 1 in the processing are taken into consideration.
Based on the above characteristics, in the case of forming a via hole 1c with a small diameter by employing a chemical method such as by etching, the interval between adjacent via holes 1c can be made narrower than that between the through holes 1d, and a circuit pattern can be formed at the portion adjacent the via hole 1c and the upper side of the via hole 1c, thus to achieve higher integration and miniaturization of the printed circuit board.
Such a via hole 1c has a conductive layer 1e and is coated with a solder resist using a screen printing process or a roller coating process to protect the conductive layer 1e from external impact and to prevent foreign materials from attaching to the conductive layer 1e. 
First, the conventional hole plugging method of the printed circuit board using the screen printing process will be described with reference to FIGS. 1A and 1B.
The structure of the printed circuit board includes circuit patterns (surface circuits patterns) 1a positioned on both the upper and lower surfaces of the board 1 and circuit patterns (internal circuits) 1b positioned in the inner layers of the board.
On the board 1, a via holes 1c is formed to electrically interconnect the surface circuit pattern 1a and internal circuit 1b through the conductive layer le, and the through hole 1d is formed to electrically interconnect both the upper and lower surface circuit patterns 1a through the conductive layer 1e. 
In the hole plugging method of the printed circuit board using the screen printing technique, the board 1 is positioned on a jig (not shown) and a screen 2 such as a mesh is positioned at the upper side thereof at a certain distance.
Then, after coating solder resist (SR) on the upper surface of the screen 2, the solder resist (SR) is discharged through an opening 2a in the screen 2 by pushing a squeegee 3 in the direction of the arrow in the drawing and then is filled in the via hole 1c and through hole 1d of the board 1.
In the above screen printing technique, the screen 2 is formed in the form of a mesh by weaving a plurality of fine wires 2b crossing each other. The wire diameter of a #110 screen is approximately 0.08 mm and the wire diameter of a #600 screen is approximately 0.045 mm. As shown in FIG. 1B, if that the diameter of the subminiature via hole is 0.1 to 0.15 mm, in the portion where the fine wires intersect, part of the via hole 1c is covered since the diameter of the conventional fine wire 2b is half that of the via hole 1c. 
Particularly, a considerable portion of the via hole 1c where the fine wires 2b cross each other is covered and accordingly, the solder resist (SR) cannot be plugged sufficiently.
Also, the solder resist (SR) is coated in the space 1f between the surface circuit pattern 1a and the screen 2 since the solder resist SR is coated by using the screen 2. However, removing the solder resist SR afterwards by an abrasive process to expose the surface circuit pattern 1a is not easy since the solder resist SR is coated covering the surface circuit pattern 1a completely and damages may result to the surface circuit pattern 1a in case of removing the solder resist SR by using a brush and the like.
Second, the conventional hole plugging method of the printed circuit board using the roller coating technique will be described with reference to FIGS. 2A and 2B.
In the hole plugging method using the roller coating after supplying the solder resist SR to an upper roller 4a and lower roller 4b, the solder resist SR at the rollers 4a and 4b is transferred to the board 1 and coated by passing the board 1 between rollers 4a and 4b at the both side thereof.
In the conventional roller coating method, the solder resist SR is coated by putting the solder resist SR in a groove (not shown) formed on the circumferential surface of the rollers 4a and 4b, but in case a projecting portion 5 with relatively small amount of solder resist SR is abutted to the via hole 1c or blocks up the via hole 1c, a sufficient amount of solder resist SR can not be plugged.
In the screen printing method, the solder resist SR is coated in the via hole 1c or the through hole 1d of the board 1 by pushing the solder resist SR coated on the screen 2 after putting the screen 2 on the board 1. In the roller coating method, the solder resist SR on the rollers 4a and 4b is flowed and coated on the via hole 1c and the through hole 1d of the board 1. Air bubbles remaining behind in the solder resist SR are discharged due to the high heat when the integrated circuit (not shown) is mounted, and accordingly the circumferential circuit patterns, solder resist and integrated circuit can be damaged even though the solder resist SR is filled in the via hole 1c and the through hole 1d. Also, the coefficients of thermal expansion of the integrated circuit and the board are different and accordingly, the board can be damaged when high heat is generated in the integrated circuit.
To solve the above problems, the present applicant had filed an earlier application for “A Method for Fabricating a Printed Circuit Board using Vacuum” (Korea Patent Application No. 2000-19045) on Apr. 11, 2000 and also an application for US Letters patent therefore, under U.S. patent application Ser. No. 09/832,122.
In the above fabrication method, the solder resist is coated on the via hole of the board, and at the same time air in the via hole is discharged to the outside and the solder resist is plugged in the via hole. The solder resist can be plugged in the via hole efficiently by completely removing the residual air bubbles in the via hole. However, there are disadvantages in the cost and the manufacturing time, in that a vacuum device must be equipped and repeated operation of exposure under the vacuum condition and plugging operations are needed thus to reduce productivity.